The month of March has not been kind to the National Football League. Two titans of the modern football era decided to announce their retirements within a span of 24 hours. Based on their football achievements, both Peyton Manning and Calvin Johnson will wait just five years (a mandatory waiting period) before enshrinement into the National Football Hall of Fame.

It may take longer, however, to fill the League's leadership vacuum.

From 2009-10, I spent two years as an assistant defensive backs coach with the Detroit Lions. When I landed in Motown, the stench of an 0-16 campaign (the only winless season in the history of the NFL) drifted over the city.

Our newly-minted head coach, Jimmy Schwartz, forced every assistant to watch every play from the previous season. To be kind, the lowlight reel was difficult to endure.

One theme kept emerging, however, from the projector screen. Calvin Johnson was not a quitter. It was easy to detect which players were “turning it down” as the losses continued to mount that season, and Johnson was not in that category. The tenacity that he displayed in the season opener was indistinguishable from the passion he showed in the final game.

Here are three life lessons gleaned from the storied career of Calvin Johnson. His journey through the NFL is a case study on grit and determination.

The defensive backs and wide receivers occupied the same region of the practice field when I coached with the Lions. During practice, I would peek at the wide receiver drills, led by one of the League’s top wide receiver coaches – Shawn Jefferson. The maneuvers looked like something from a Navy SEAL training session. The drills were nonstop and frenetic.

Every single drill featured one constant – Calvin Johnson at the head of the line. Whether we were in the dog days of training camp or in the frigid temperature of December, Calvin Johnson was the first receiver in line for every single drill.

To put this level of dedication in perspective, one must consider that wide receivers run more during the course of a game than nearly every other player on the roster. As a receiver’s odometer logs more and more miles over time, it is common for some players to hit the “cruise control” button.

Cruising allows the body to conserve energy and generate a few more seasons in the final phase of one’s career. The tendency to coast is human nature. The outliers of society – the Calvin Johnson’s of this world – lack an internal governor. Every time these over-achievers take a seat at life’s poker table, they are poised to push all of the chips to the middle. And that “all-in” mentality is precisely why they finish at the top.

Key Takeaway: If you want to play at the front, you have to practice at the front.